JP2010122484A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display achieved in display having memory performance at a low voltage. <P>SOLUTION: The liquid crystal display 11 includes: a liquid crystal display medium 20 that has a liquid crystal layer 23 disposed between a pair of electrodes 22 and 25 disposed facing each other, and displays an image by reflecting or transmitting external light according to the orientation of the liquid crystal layer; and an electrostatic actuator 30 disposed at a side opposite to the display surface of the liquid crystal display medium. The liquid crystal display displays the image by changing the orientation of the liquid crystal layer by the application of a voltage to a specific area of the liquid crystal display medium through the pair of electrodes according to image data after the orientation of the crystal layer is changed to a planar state by applying stress to the liquid crystal display medium by the electrostatic actuator. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device.

  By having a cholesteric liquid crystal layer between a pair of electrodes and applying a driving voltage, the orientation pattern of the cholesteric liquid crystal layer is changed to a focal conic phase (F phase), a planar phase (P phase), or a homeotropic phase (H A medium (for example, electronic paper) has been proposed in which an image is displayed by appropriately changing the phase) and reflecting or transmitting external light.

In a display device using such a cholesteric liquid crystal layer, a high reflectance and a low driving voltage are required. For example, in order to eliminate the need for an erasing voltage, there has been proposed a display device that erases an image by applying a pressure to a part between substrates sandwiching a liquid crystal layer to create a flow of the liquid crystal layer (see Patent Document 1). In addition, there has been proposed a recording medium that includes a heat-sensitive shape memory material layer and a cholesteric liquid crystal layer and performs drawing by temperature change using a thermal head or laser light (see Patent Document 2).
JP 2005-501294 Gazette JP 2002-006280 A

  An object of the present invention is to provide a liquid crystal display device that realizes a display with a low voltage and a memory property.

According to a first aspect of the present invention, there is provided a liquid crystal display medium in which a cholesteric liquid crystal layer is disposed between a pair of opposed electrodes, and an image is displayed by reflecting or transmitting external light depending on the alignment state of the liquid crystal layer, and the liquid crystal display An electrostatic actuator disposed on the side opposite to the display surface of the medium, and applying pressure to the liquid crystal display medium by the electrostatic actuator to bring the liquid crystal layer into a planar state, Accordingly, a voltage is applied to the specific area of the liquid crystal display medium through the pair of electrodes to change the alignment state of the liquid crystal layer and display an image.
According to a second aspect of the present invention, the liquid crystal display medium has a partition that partitions the liquid crystal layer between the electrodes, and the electrostatic actuator has a partition at a position corresponding to the partition of the liquid crystal display medium. The liquid crystal display device according to claim 1.
The invention of claim 3 is characterized in that the liquid crystal display medium has a structure in which a plurality of liquid crystal layers that selectively reflect light in different wavelength ranges are laminated. Liquid crystal display device.

According to the first aspect of the present invention, it is possible to provide a liquid crystal display device that realizes a display with a low voltage and a memory property as compared with the case without this configuration.
According to the second aspect of the present invention, it is possible to provide a liquid crystal display device that can more reliably realize a display with a low voltage and a memory property as compared with the case where this configuration is not provided.
According to the third aspect of the present invention, it is possible to provide a liquid crystal display device that has a low voltage and a memory property and realizes multicolor display as compared with the case without this configuration.

  Hereinafter, embodiments will be specifically described with reference to the accompanying drawings. It should be noted that members having substantially the same functions and actions are given the same reference numerals or symbols throughout the drawings as appropriate, and redundant descriptions are omitted as appropriate.

  First, alignment characteristics of cholesteric liquid crystal will be described. FIG. 1 schematically shows the alignment state of the cholesteric liquid crystal. Cholesteric liquid crystal has a characteristic that liquid crystal molecules are arranged in layers and each layer has a spiral twisted structure. Among the light incident from the direction of the helical axis of the cholesteric liquid crystal layer having such a helical structure, specific light depending on the helical pitch is interference-reflected, and the orientation changes depending on the electric field strength, thereby changing the reflectance. Specifically, a planar phase in which the helical axis is substantially perpendicular to the cell surface and selectively reflects light of a specific wavelength with respect to incident light (FIG. 1A), and the helical axis is substantially on the cell surface. A focal conic phase (FIG. 1 (B)) that is parallel and transmits incident light while being forward scattered, and a homeotropic phase (FIG. 1 (C)) that unwinds the helical structure and transmits the incident light almost completely. The three states are shown.

In such a reflection type liquid crystal display device using cholesteric liquid crystal, generally, after applying a voltage higher than a threshold value for homeotropic alignment, it rapidly becomes planar alignment when the electric field is removed, and the cholesteric liquid crystal has a helical pitch. Corresponding reflection color will be shown. However, once passing through homeotropic alignment, an expensive drive IC is required because of a high drive voltage, and there is a problem that the number of drive ICs drastically increases and the cost increases with the increase in definition. In addition, in the planar alignment state by an electric field, there is a problem that the reflectivity is low and the original reflectivity of the liquid crystal cannot be sufficiently utilized. Therefore, in order to obtain a sufficient reflectance, it is necessary to increase the thickness of the liquid crystal layer, and as a result, the drive voltage becomes high.
On the other hand, if the cholesteric liquid crystal layer is brought into a planar state by applying pressure, the reflectance can be increased as compared with the case where the planar alignment state is brought about by an electric field.

  FIG. 2 shows a case where the cholesteric liquid crystal layer (thickness: 2 μm) is initialized by applying a pressure (characteristic curve connecting rhombus plots) and a case where it is initialized by applying a voltage (20 V) (characteristic curve connecting square plots). The drive voltage-reflectance characteristic when writing is performed by applying a certain rectangular voltage for 300 ms is shown. As shown in FIG. 2, the orientation state of the cholesteric liquid crystal changes from the voltage exceeding the planar state (P), the focal conic state (Fc), and the homeotropic state again to the planar state (P) according to the electric field strength. To do.

Normally, when image writing is performed only by voltage, the liquid crystal layer in a specific region is written by changing the alignment state from the homeotropic state to the planar state (P ′) or the focal comic state (Fc). Even if the thickness of the layer is reduced to about 2 μm, a driving voltage of at least about 20 V is required.
On the other hand, when the liquid crystal layer is brought into a planar state (P) by pressure, a high reflectance is obtained in the planar state, and a focal conic state (Fc) is obtained at about 10V. That is, after the entire liquid crystal layer is brought into a planar state (P) by pressure, a voltage of about 10 V is applied to a specific region corresponding to the image data to change the reflectance in a focal conic state (Fc), thereby writing an image. It can be performed.

<First Embodiment>
FIG. 3 schematically shows the liquid crystal display device according to the first embodiment. The liquid crystal display device 11 according to the present embodiment includes a liquid crystal display medium 20 and an electrostatic actuator 30. The electrostatic actuator 30 is disposed on the opposite side of the display surface of the liquid crystal display medium 20 and is integrated with the liquid crystal display medium 20. In the liquid crystal display device 11 having such a configuration, stress is applied to the liquid crystal layer 23 of the liquid crystal display medium 20 by the electrostatic actuator 30 to form a planar state, and then image data is transmitted through the pair of electrodes 22 and 25 of the liquid crystal display medium 20. When a voltage is applied to a specific area corresponding to the above, the alignment state of the liquid crystal layer 23 is changed to display an image. Further, since the image is held with no power supply except when the image is written, it is possible to display an image with a low voltage.

(Liquid crystal display medium)
FIG. 4 schematically shows the configuration of the liquid crystal display medium 20. The liquid crystal display medium 20 has two substrates 21 and 26 each having electrodes 22 and 25 formed on one side, and a cholesteric liquid crystal layer (referred to as a “liquid crystal layer”) 23 between the pair of electrodes 22 and 25. Has been placed. Depending on the alignment state of the liquid crystal layer 23, external light (incident light) is reflected or transmitted to display an image.

-Board-
Each of the substrates 21 and 26 is composed of a sheet-like member that holds the liquid crystal layer 23 and the like therebetween and has strength to withstand external force.
Specific materials constituting the substrates 21 and 26 include inorganic sheets (for example, glass and silicon substrates), polymer films (for example, polyethylene terephthalate, polysulfone, polyethersulfone, polycarbonate, and polyethylene naphthalate). For example, when the liquid crystal display device according to this embodiment is an electronic paper, the substrates 21 and 26 are preferably flexible, and a polymer film is suitable.

The substrate 21 on the display surface side is a transparent substrate that transmits at least incident light and can visually observe an image displayed according to the alignment state of the liquid crystal layer 23. Usually, a transparent substrate having transparency over the entire visible light region may be used, but a transparent substrate having light transmittance only in a specific wavelength range to be displayed may be used. Moreover, you may form well-known functional films, such as a pollution protection film, an abrasion-resistant film | membrane, a light reflection prevention film, and a gas barrier film, on an outer surface.
Although the thickness of the substrate 21 on the display surface side depends on the material and the like, it is usually set to about 0.025 to 2 mm in consideration of strength, flexibility and the like for protecting the liquid crystal layer 23 and the like.

On the other hand, a light absorbing layer 27 that absorbs light transmitted through the liquid crystal layer 23 is formed on the non-display-side substrate 26 that is in contact with the electrostatic actuator 30. The light absorption layer 27 uses a black color material that absorbs the entire visible wavelength range (400 to 700 nm), for example, a paint containing a black pigment or black dye such as carbon black or aniline black, or an inorganic material such as chromium oxide. Formed.
The thickness of the substrate 26 on the non-display side needs to be a thickness at which the stress due to the electrostatic actuator 30 is transmitted to the liquid crystal layer 23 and is usually about 25 to 200 μm although it depends on the material and the like.

-Electrode-
The liquid crystal display device according to the present embodiment is a passive matrix type, and striped electrodes 22 and 25 are formed on the substrates 21 and 26, respectively, so that one is an anode and the other is a cathode. The stripe electrodes 22 and 25 are arranged so as to intersect with each other, and a voltage is applied to the liquid crystal layer 23 in a region where the electrodes 22 intersect. By applying a voltage to the liquid crystal layer 23 through the electrodes 22 and 25 in a specific region corresponding to the image data, the alignment state is changed, whereby the reflectance for light of a specific wavelength is changed.

  Specifically, as the electrodes 22 and 25, metal (for example, gold, aluminum), metal oxide (for example, indium oxide, tin oxide, indium tin oxide (ITO)), conductive organic polymer (for example, polythiophene-based, polyaniline) For example, a conductive thin film formed by a system) can be used. The electrode on the display surface side is a transparent electrode that transmits at least incident light. The transparent electrode may be transparent over the entire visible light range, or may be transparent only in the wavelength range to be displayed. From the viewpoints of light transmittance and film formability, an ITO electrode is preferable.

-Alignment film-
An alignment film (not shown) is formed on the electrodes 22 and 25. The alignment film is a film for aligning liquid crystal molecules in a certain direction. In this embodiment, a vertical alignment film for making the alignment state of the liquid crystal layer 23 focally conical is provided. For the formation of the alignment film, a resin such as polyimide or polyvinyl alcohol, a low molecular surface modifier such as an alkyl ammonium compound or an alkyl silane compound, an inorganic thin film such as SiO, or the like is used. For example, the vertical alignment film can be formed by forming a groove on the electrode film using a resin material such as polyimide resin and then forming grooves in a certain direction by rubbing.

-Bulkhead-
A partition wall (rib) 24 that partitions the liquid crystal layer 23 is formed between the upper and lower electrodes 22 and 25. For example, by forming a grid-like partition wall 24 between the upper and lower electrodes 22 and 25, the liquid crystal layer 23 surrounded by the partition wall 24 forms a pixel.
The partition wall 24 is formed, for example, by applying a negative resist or a positive resist on the alignment film formed on the transparent substrate 21, exposing to a predetermined pattern using a photomask, and developing the resist pattern.

-Liquid crystal layer-
The liquid crystal layer 23 is mainly composed of cholesteric liquid crystal. The liquid crystal layer 23 is disposed in a state of being partitioned by the partition wall 24 between the opposed electrodes 22 and 25, and the alignment state of the liquid crystal layer 23 in a specific region changes, so that light having a specific wavelength in incident light is changed. The reflection / transmission state is modulated. In addition, the selected alignment state is maintained without application of voltage due to the memory property that is a characteristic of the cholesteric liquid crystal.

  Specific liquid crystals that can be used as cholesteric liquid crystals include nematic liquid crystals (eg, Schiff base, azo, azoxy, benzoate, biphenyl, terphenyl, cyclohexylcarboxylate, phenylcyclohexane, biphenyl). Cyclohexane, pyrimidine, dioxane, cyclohexyl cyclohexane ester, cyclohexyl ethane, cyclohexane, tolan, alkenyl, stilbene, condensed polycyclic), or mixtures thereof, and chiral agents (eg, steroid cholesterol derivatives) , Schiff base, azo, ester, biphenyl) and the like.

The helical pitch of the cholesteric liquid crystal is adjusted by the amount of chiral agent added to the nematic liquid crystal. For example, when the display color is blue, green, or red, the nematic liquid crystal and the chiral agent are set so that the center wavelength of selective reflection is, for example, in the range of 400 nm to 500 nm, 500 nm to 600 nm, or 600 nm to 700 nm. What is necessary is just to adjust a compounding quantity.
Further, in order to compensate for the temperature dependence of the helical pitch of the cholesteric liquid crystal, a known method of adding a plurality of chiral agents having different twist directions or opposite temperature dependence may be used.

(Electrostatic actuator)
FIG. 5 schematically shows the configuration of the electrostatic actuator 30. The electrostatic actuator 30 according to the present embodiment is an opposing flat plate type, and is integrated with the liquid crystal display medium 20 behind the display surface of the liquid crystal display medium 20 (on the side opposite to the display surface). Electrodes 32 and 35 are respectively formed on the substrates 31 and 36 arranged to face each other, and the upper substrate 31 is deformed by applying a voltage between the electrodes 32 and 35. Since the electrostatic actuator 30 is integrated with the liquid crystal display medium 20, stress is applied to the liquid crystal display medium 20 with the deformation of the upper substrate 31 of the electrostatic actuator 30, so that the liquid crystal layer 23 is brought into a planar state. it can.

-Board-
The upper substrate 31 of the electrostatic actuator 30 is configured to move up and down depending on whether or not a voltage is applied between the electrodes 32 and 35. For example, in addition to the polymer material mentioned as the material constituting the substrates 21 and 26 of the liquid crystal display medium 20, there may be mentioned polyvinylidene chloride, polyvinyl chloride, chlorinated polyolefin, polyolefin and the like. The thickness of the upper substrate 31 is usually about 1 to 25 μm so that it can move up and down and stress can be applied to the liquid crystal display medium 20 depending on the material and the like.

  On the other hand, the back substrate 36 hardly deforms even when a voltage is applied between the electrodes 32 and 35. Specific examples of the material of the rear substrate 36 include the materials described as materials constituting the substrates 21 and 26 of the liquid crystal display medium. Examples include molecular materials. Although the thickness of the back substrate 36 depends on the material and the like, it is usually set to about 50 μm to 2 mm in order to prevent deformation when a voltage is applied.

-Electrode-
The upper and lower electrodes 32 and 35 constituting the electrostatic actuator 30 are not particularly limited as long as they have conductivity. For example, the upper and lower electrodes 32 and 35 are formed of the same conductive material as the electrodes 22 and 25 constituting the liquid crystal display medium 20. Is done. In view of conductivity, film formability, etc., an Al electrode is particularly preferable. Since the electrostatic actuator 30 applies stress to the entire liquid crystal layer of the liquid crystal display medium 20 at once, the upper and lower electrodes 32 and 35 are formed as common electrodes on one entire surface of each of the substrates 31 and 36, respectively. The

-Bulkhead-
A partition wall 34 is provided between the substrates 31 and 36 of the electrostatic actuator 30 at a position corresponding to the partition wall 24 that partitions the liquid crystal layer 23 of the liquid crystal display medium 20. Here, the “corresponding position” means that the substrate 31 is located at substantially the same position when viewed from above, specifically, between the electrodes 32 and 35 of the electrostatic actuator 30. It means a position where the vertical movement of the central substrates 31 and 26 is not suppressed by the presence of the partition wall 24 of the liquid crystal display medium 20 when a voltage is applied.
If the same mask as that used for forming the partition wall 24 of the liquid crystal display medium 20 is used, the partition wall 34 can be formed in the same pattern. Examples of the material constituting the partition wall 34 include a negative resist or a positive resist. Air is sealed in the space between the substrates 31 and 36 partitioned by the partition wall 34.
The partition 34 on the electrostatic actuator 30 side is not essential, but the partition 34 is also provided between the substrates 31 and 36 of the electrostatic actuator 30 corresponding to the partition 24 of the liquid crystal layer 23 of the liquid crystal display medium 20. Then, when a voltage is applied between the electrodes 32 and 35 of the electrostatic actuator 30, stress is applied more evenly to the individual liquid crystal layers 23 partitioned by the partition walls 24 on the liquid crystal display medium 20 side. The entire liquid crystal layer 23 can be initialized more reliably (planar alignment state generation).

  In the electrostatic actuator 30 having such a configuration, the electrostatic force is inversely proportional to the square of the gap interval. Accordingly, in order to obtain a large force at a low voltage, the electrode interval d may be reduced. For example, the stress generated by the electrostatic actuator 30 increases as the thickness of the upper substrate 31 decreases. In the present embodiment, the electrode 32 of the upper substrate 31 is disposed so as to face the liquid crystal display medium 20, and the upper substrate 31 is interposed between the electrodes 32 and 35. Although a short circuit between the electrodes 32 and 35 is prevented, the electrodes 32 and 35 of the substrates 31 and 36 may be opposed to each other, and an insulator may be disposed between the electrodes 32 and 35 to prevent the short circuit.

The surface of the liquid crystal display medium 20 on the light absorption layer 27 side and the surface on which the upper electrode 32 of the electrostatic actuator 30 is formed are bonded together via an adhesive layer (not shown). At this time, the liquid crystal display medium 20 is bonded so that the position of the partition wall 24 and the position of the partition wall 34 of the electrostatic actuator 30 coincide with each other. Thereby, the reflective liquid crystal display device 11 according to the present embodiment is obtained.
In the liquid crystal display device 11 according to the present embodiment, stress is applied to the liquid crystal layer 23 of the liquid crystal display medium 20 by applying a voltage between the electrodes 32 and 35 of the electrostatic actuator 30 to deform the upper substrate 31. The liquid crystal layer 23 is in a planar alignment state and reflects incident light, so that the entire surface of the liquid crystal display medium 20 displays white.

  In this way, after the liquid crystal layer 23 is brought into a planar state by the electrostatic actuator 30 and is collectively reset, for example, the electrodes of the liquid crystal display medium 20 according to image data from the outside such as a main controller that controls input / output of image data. A voltage is applied to a specific region between 22 and 25. In the liquid crystal layer 23 to which a voltage is applied, the planar alignment state changes to the focal conic state. In the focal conic state, the helical axis of the helical structure is substantially parallel to the substrate surface, and incident light is transmitted through the liquid crystal layer 23. Therefore, in the liquid crystal layer 23 in the focal conic state, incident light is transmitted through the liquid crystal layer 23 and absorbed by the light absorption layer 27, and a dark display (black display) is selectively formed.

In this way, an image is displayed by changing the liquid crystal layer 23 in a specific area corresponding to the image data from the planar state to the focal conic state. For example, if the thickness of the liquid crystal layer 23 is 2 μm, the focal state is changed from the planar state. The change to the state is realized with a low voltage of about 10V. That is, the liquid crystal layer 23 of the liquid crystal display medium 20 is initialized as a planar alignment state by applying stress from the electrostatic actuator 30, and then the liquid crystal layer 23 in a specific region is set to the focal conic state based on image data input from the outside. As a result, image writing is performed at a low voltage.
Therefore, for example, in the conventional liquid crystal display device that is driven only by the electric field between the electrodes of the liquid crystal display medium, the liquid crystal display device 11 according to the present embodiment is compared with the case where a drive IC capable of outputting a drive voltage of about 40 V is required. The voltage for driving the electrostatic actuator 30 requires a large voltage depending on the configuration, but can be driven by a driving IC capable of outputting a driving voltage of about 10 V, and the cost can be greatly reduced. .

<Second Embodiment>
FIG. 6 shows a liquid crystal display device according to the second embodiment. In the liquid crystal display device 12 according to the present embodiment, the first liquid crystal layer 23a and the second liquid crystal layer 23b are laminated via the transparent substrate 26a in the liquid crystal display medium, and one is a left-handed liquid crystal layer, The other is a right-handed liquid crystal layer. Each liquid crystal layer 23a, 23b is disposed between separate electrodes 22a, 25a, 22b, 25b, and is partitioned by partition walls 24a, 24b formed in a corresponding pattern. The configuration of the electrostatic actuator 30 is the same as that of the first embodiment.

  The planar phase of the cholesteric liquid crystal is a selective reflection phenomenon that splits light incident parallel to the helical axis into right-handed and left-handed light, Bragg-reflects circularly polarized light components that coincide with the helical twist direction, and transmits the remaining light. Wake up. Therefore, in either the right-handed rotation or the left-handed right-handed liquid crystal layer, about half of the incident light is transmitted without being reflected.

  On the other hand, as shown in FIG. 6, if the left-handed and right-handed liquid crystal layers 23a and 23b are stacked, the reflectance is improved as compared with the case of a single layer, so that a brighter display is possible. At the same time, the contrast is improved. Each liquid crystal layer 23a, 23b is driven separately by electrodes 22a, 25a, 22b, 25b sandwiching each liquid crystal layer 23a, 23b. Accordingly, since the two liquid crystal layers 23a and 23b stacked in the same pixel can be driven separately to have different alignment states, the reflectance can be adjusted to other stages as compared with the case of a single layer. Is possible.

Note that when the transparent substrate 26a disposed between the two liquid crystal layers 23a and 23b has a large retardation (phase difference), the light transmitted through the first liquid crystal layer 23a is deflected by turning around inside the substrate. Or the transmittance | permeability falls. Therefore, it is preferable that the transparent substrate 26a between the liquid crystal layers has a small retardation, and specifically, it is composed of one or more selected from polyethersulfone, polycarbonate, polyvinyl chloride, polyvinylidene chloride and cyclic polyolefin. Polyether sulfone is particularly preferable.
Further, the thickness of the transparent substrate 26a is set to about 1 to 25 μm in order to suppress a decrease in light transmittance and an increase in driving power of the electrostatic actuator 30 when the liquid crystal layers 23a and 23b are initialized. Good.

  The liquid crystal layers 23a and 23b are initialized at the same time because stress is simultaneously applied by the electrostatic actuator 30. However, the liquid crystal layers 23a and 23b are initialized by pressing each liquid crystal layer by providing an electrostatic actuator for each liquid crystal layer. It is good. In the case of such a configuration, the substrate and electrodes of the electrostatic actuator disposed between the liquid crystal layers 23a and 23b may be made of a light transmissive material.

<Third Embodiment>
FIG. 7 shows a liquid crystal display device according to the third embodiment. In the liquid crystal display device 13 according to the present embodiment, the first liquid crystal layer 23a and the second liquid crystal layer 23b are laminated via a light transmissive film 29, one of which is a left-handed liquid crystal layer, and the other Is a right-handed liquid crystal layer. The liquid crystal layers 23a and 23b are disposed between the same electrodes 22 and 25, and the liquid crystal layers 23a and 23b are driven simultaneously. The configuration of the electrostatic actuator 30 is the same as that of the first embodiment, and the two liquid crystal layers 23a and 23b are simultaneously reset by being stressed.

  In the liquid crystal display device 13 according to the present embodiment, since the two liquid crystal layers 23a and 23b are disposed between the same electrodes 22 and 25 and are driven simultaneously, the driving voltage is higher than that of the liquid crystal display device 12 according to the second embodiment. However, since no electrode is interposed between the two liquid crystal layers 23a and 23b, the light transmittance is increased and the contrast can be further improved.

<Fourth Embodiment>
FIG. 8 shows a liquid crystal display device according to the fourth embodiment. In the liquid crystal display device 14 according to the present embodiment, three liquid crystal layers 23B, 23G, and 23R that selectively reflect light (blue, green, or red) in different wavelength ranges in the liquid crystal display medium are stacked. Transparent substrates 26a and 26b are provided between the liquid crystal layers 23B, 23G, and 23R. As in the second embodiment, the liquid crystal layers 23B, 23G, and 23R are respectively independently driven electrodes 22a and 25a. , 22b, 25b, 22c, and 25c, and partitioned by partition walls 24a, 24b, and 24c, respectively. Since the display colors of the liquid crystal layers 23B, 23G, and 23R depend on the helical pitch of the cholesteric liquid crystal, the center wavelengths of selective reflection of the layers 23B, 23G, and 23R are, for example, 400 nm to 500 nm (blue), 500 nm to 600 nm (green) ), Or the blending amount of the nematic liquid crystal and the chiral agent may be adjusted to be in the range of 600 nm to 700 nm (red).

  When performing color display in this way, a filter or a light absorption layer may be formed on one side of the liquid crystal layers 23B, 23G, and 23R as necessary. When the display surface is viewed from an oblique direction, the wavelength of light reflected by each liquid crystal layer may change and appear different colors. In particular, in a liquid crystal layer that reflects light having a red wavelength, the reflected wavelength moves greatly, and the reflected light moves to the short wavelength side (so-called blue shift), so that the display becomes difficult to see. For example, the blue shift is suppressed by providing a red filter between the liquid crystal layer 23G that should reflect green light and the liquid crystal layer 23R that should reflect red light.

  For example, PD400R / FX1 manufactured by Hitachi Chemical Co., Ltd. as a red filter, Optomer SS2191 manufactured by JSR Co., Ltd., Kayase Yellow K-CL (1 wt%) manufactured by Nippon Kayaku Co., Ltd., and JSR as a filter for yellow reflective layer Optomer SS2191 / manufactured by Nippon Kayaku Co., Ltd., Kayase Orange A-N (1 wt%) is used.

In the liquid crystal display device 14 according to the present embodiment, the voltages applied to the liquid crystal layers 23B, 23G, and 23R can be controlled independently. Therefore, the alignment state of the liquid crystal layers 23B, 23G, and 23R, that is, the reflection -Full color display is possible by controlling the transmission state independently. However, in this embodiment, an electrostatic actuator may be provided for each of the liquid crystal layers 23B, 23G, and 23R, and initialization may be performed for each liquid crystal layer.
The selective reflection wavelength of each liquid crystal layer is not limited to the above three colors, and may be a structure in which two liquid crystal layers that selectively reflect light in different wavelength ranges are laminated, or a structure in which four or more layers are laminated. Also good.

Examples will be described below.
<Production of liquid crystal display medium>
-Electrode formation-
Two polyethersulfone (PES) films (manufactured by Sumitomo Bakelite Co., Ltd., 100 μm thickness, 100 Ω / sq.) Having an ITO film formed on one side are prepared, and 5 strip-shaped electrodes each having a width of 1 cm are provided at intervals of 1 mm. The ITO film was patterned so as to be arranged in parallel.

-Formation of alignment film-
SE7511L (Nissan Chemical Co., Ltd., for vertical alignment) was diluted 10 times with ethyl cellosolve. This solution was spin-coated on the surface of each substrate on which the ITO electrode was formed, and then heated to form a vertical alignment film.

-Rib formation-
A negative resist KI1000-V10 (manufactured by Hitachi Chemical Co., Ltd., 4 μm thickness) was spin-coated on the alignment film formed on one substrate. Development was carried out after exposure through a photomask. As a result, rib patterns having a width of 1 mm were formed at intervals of 1 cm in length and width.

-Formation of liquid crystal layer-
The PES film formed up to the ribs and the film formed up to the alignment film were opposed so that the strip-shaped electrodes formed on each film were orthogonal to each other. Then, the liquid crystal composition was laminated between the films, and the peripheral portions of the two substrates were bonded together via a UV curable resin and UV cured.
As the liquid crystal, E44 (host nematic liquid crystal, manufactured by Merck & Co., Inc.) was used. Moreover, R-811 and R-1011 (made by Merck) are used as a chiral agent, and each mixing ratio is 811/1011 = 4/1. The mixing ratio of the chiral agent in the entire liquid crystal composition with respect to each color is, for example, 23 wt% for blue (440 nm), 20.2 wt% for green (520 nm), and (610 nm) for red (16 nm). 8 wt%.

<Production of electrostatic actuator>
-Electrode formation-
Aluminum was deposited on one side of a 250 μm thick PES film.

-Rib formation-
Next, ribs (thickness: 5 μm) were formed on the Al film using SU-8 (epoxy resin, MicorChem). At this time, the same rib pattern as the liquid crystal display medium was formed using the photomask used for forming the rib in the liquid crystal display medium.

-Laminating films-
Next, aluminum was deposited on a 12 μm-thick saran resin (vinylidene chloride resin) film to form an Al film, and the saran resin film and the PES film were laminated so that the saran resin surface was on the rib side of the PES film. . This produced the electrostatic actuator.

<Integration of liquid crystal display medium and electrostatic actuator>
The surface on the light absorption layer side of the liquid crystal display medium and the Al surface formed on the Saran resin film of the electrostatic actuator were laminated together. As a result, a liquid crystal display device having a configuration as shown in FIG. 1 was manufactured. This liquid crystal display device was able to display with a driving voltage of about 5 Hz and 50 V for driving an electrostatic actuator for initialization (planar alignment) and a driving voltage of about 50 Hz and 23 V for focal conic alignment of liquid crystal.

  The present invention is not limited to the above embodiments and examples, and may be modified as appropriate. For example, in the above embodiment and example, the liquid crystal display medium and the electrostatic actuator are separately manufactured and bonded to form a liquid crystal display device. For example, as shown in FIG. The liquid crystal display device 15 may be integrated through the same substrate 28. For example, if a substrate on which a light absorption layer is formed or a substrate having light absorption is used, an electrode 25 of a liquid crystal display medium is formed on one surface and an electrode 32 of an electrostatic actuator is formed on the other surface. Good. With the liquid crystal display device having such a configuration, it is possible to further reduce the thickness and weight, and the stress due to the electrostatic actuator is more easily transmitted to the liquid crystal layer 23, and the batch reset is further facilitated.

  In addition, the liquid crystal display medium and the electrostatic actuator may use a common electrode. For example, as shown in FIG. 10, the substrate 21 on the display side of the liquid crystal display medium is provided with an active type pixel electrode 22A partitioned by a matrix-like partition wall 24, and between the liquid crystal display medium and the electrostatic actuator. A common substrate 26 provided with a common electrode 25A is provided on the surface on the liquid crystal display medium side. The common electrode 25A may be provided on the surface of the common substrate 26 on the electrostatic actuator side. Also in the liquid crystal display device 16 according to the present embodiment, when a voltage is applied between the electrodes 25A and 35 to deform the central substrate 26, stress is applied to the liquid crystal layer 23 of the liquid crystal display medium, and the liquid crystal layer 23 is brought into a planar state. After that, the voltage is applied to the specific area corresponding to the image data through the electrodes 22A and 25A, whereby the orientation state of the liquid crystal layer 23 is changed and the image is displayed. The image is held with no power supply except when the image is written. Therefore, image display at a low voltage is possible.

It is a figure which shows typically the orientation state of a cholesteric liquid crystal. (A) Planar phase (B) is the focal conic phase (C) Homeotropic phase It is a figure which shows the drive voltage-reflectance characteristic in case the thickness of a cholesteric liquid crystal layer is 2 micrometers. It is the schematic which shows the structure of the liquid crystal display device which concerns on 1st Embodiment. It is the schematic which shows the structure of a liquid crystal display medium. It is the schematic which shows the structure of an electrostatic actuator. It is the schematic which shows the structure of the liquid crystal display device which concerns on 2nd Embodiment. It is the schematic which shows the structure of the liquid crystal display device which concerns on 3rd Embodiment. It is the schematic which shows the structure of the liquid crystal display device which concerns on 4th Embodiment. It is the schematic which shows the structure of the liquid crystal display device which concerns on 5th Embodiment. It is the schematic which shows the structure of the liquid crystal display device which concerns on 6th Embodiment.

Explanation of symbols

11, 12, 13, 14, 15, 16 Liquid crystal display device 20 Liquid crystal display medium 21, 26 Substrate 22, 22a, 22b, 22c, 22A Electrode 23, 23a, 23b, 23B, 23G, 23R Liquid crystal layer 24, 24a, 24b , 24c Partition 25, 25a, 25b, 25c, 25A Electrode 26, 26a, 26b, 26c Substrate 27 Light absorbing layer 28 Substrate 29 Film 30 Electrostatic actuator 31 Substrate 32 Electrode 34 Partition 35 Electrode 36 Substrate

Claims (3)

A liquid crystal display medium in which a cholesteric liquid crystal layer is disposed between a pair of opposed electrodes, and an image is displayed by reflecting or transmitting external light depending on an alignment state of the liquid crystal layer;
An electrostatic actuator disposed on the opposite side of the display surface of the cholesteric liquid crystal display medium,
By applying pressure to the liquid crystal display medium by the electrostatic actuator to bring the liquid crystal layer into a planar state, a voltage is applied to the specific area of the liquid crystal display medium through the pair of electrodes according to image data. A liquid crystal display device, wherein an image is displayed by changing an alignment state of the liquid crystal layer.   2. The cholesteric liquid crystal display medium has a partition that partitions the liquid crystal layer between the electrodes, and the electrostatic actuator has a partition at a position corresponding to the partition of the liquid crystal display medium. A liquid crystal display device according to 1.   The liquid crystal display device according to claim 1, wherein the liquid crystal display medium has a structure in which a plurality of liquid crystal layers that selectively reflect light in different wavelength ranges are stacked.

Images